Compact and high-performing microwave clocks for industrial applications

Precise timing is essential for synchronising telecommunication networks and power transmission grids, timestamping financial services, and enabling satellite navigation. The accuracy of atomic clock technologies – where time measurement is based on the frequency of electronic transitions in atoms – is increasing, and optical atomic clocks have become the most accurate timing instruments ever created. But for wider use in industry and commerce, atomic clocks need to be more compact and easier to operate, whilst also offering increased accuracy and reliability. Development and extension of new clock technologies, such as Rubidium (Rb) vapourcell clocks operating at microwave frequencies, are needed if industrial requirements for reliability, low power consumption, and good frequency stability are to be met.

The EMRP project Compact and high-performing microwave clocks for industrial applications investigated emerging clock technologies and designs with the potential to provide compact, highly accurate time and frequency references for next generation satellite navigation systems.

The project:

• Compared the performance of prototype atomic clocks to select the best clocks for further development. A pulsed optical pumping (POP) Rb-clock, the RUBICLOCK/HORACE clock based on cooled caesium (Cs) atoms, and a pulsed Cs coherent population trapping (CPT) clock were selected for further development.
• Developed a simplified POP clock with a more compact vapour cell and laser system that makes the clock frequency very stable.
• Redesigned and developed an improved version of the RUBICLOCK based on laser-based optical cooling, simplified optical components, and a redesigned microwave cavity that provides greater frequency stability than previously possible.
• Assembled and characterised an innovative CPT clock prototype using industrial components with smaller volume and lower power requirements than previously possible. The prototype demonstrated good frequency stability over an extended measurement time (100 seconds), whilst performance limitations were being identified.

The production of commercial atomic clocks for industry that can achieve comparable performance to the hyper accurate NMI clocks used for maintaining the international time standard has been brought nearer to fruition as a result of this project.

A significant project outcome has been the development of different prototype atomic clock technologies towards future commercialisation. This has been made possible by an intensive and extensive collaboration between leading European atomic clock experts, from National Measurement Institutes (NMIs), to academia. Joint research has improved key clock component design, assembly, and testing. The project has generated a better understanding and greater control of the small physical changes that are key to achieving atomic clock stability and precise timekeeping.

The RUBICLOCK prototype has been commercialised by French company Muquans, whilst another prototype POP clock is undergoing further development as a potential candidate for use in the next generation of Galileo satellites – the European Global Navigation Satellite System. This system will provide Europe with independent and secure telecommunications. Improved time and frequency standards are also critical for greater synchronisation and timekeeping in business and commerce.